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    <title>Document</title>
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    <script>
        // 类型错误
        // 1. 非函数使用new方法调用
        // Uncaught TypeError: "abc" is not a constructor
        // let n = new "abc";
        // console.log(n);

        

        // 2. 将变量作为一个函数来使用
        // Uncaught TypeError: a is not a function
        // let a = 123;
        // a()
        
       
        // 3. 调用"空对象/undefined"下不存在的属性
        // Uncaught TypeError: Cannot read properties of undefined
        // let obj = undefined;
        // console.log(obj.username);

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